This paper examines for the first time the potential complementary imaging capabilities of Optical coherence tomography (OCT) and non-linear microscopy (NLM) for multi-modal 3D examination of paintings following the successful application of OCT to the in situ, non-invasive examination of varnish and paint stratigraphy of historic paintings and the promising initial studies of NLM of varnish samples. OCT provides image contrast through the optical scattering and absorption properties of materials, while NLM provides molecular information through multi-photon fluorescence and higher harmonics generation (second and third harmonic generation). OCT is well-established in the in situ non-invasive imaging of the stratigraphy of varnish and paint layers. While NLM examination of transparent samples such as fresh varnish and some transparent paints showed promising results, the ultimate use of NLM on paintings is limited owing to the laser degradation effects caused by the high peak intensity of the laser source necessary for the generation of nonlinear phenomena. The high intensity normally employed in NLM is found to be damaging to all non-transparent painting materials from slightly scattering degraded varnish to slightly absorbing paint at the wavelength of the laser excitation source. The results of this paper are potentially applicable to a wide range of materials given the diversity of the materials encountered in paintings (e.g. minerals, plants, insects, oil, egg, synthetic and natural varnish).

An optical technique for measuring the velocity of an accelerating, specularly reflecting surface from a position on the axis of motion has been successfully applied to a free surface velocity measurement of an impacted projectile in a pneumatic accelerator. The technique combines a laser light source, a surface tilt-insensitive, lensless optical configuration, and a Fabry-Perot spectrometer to obtain a velocity-time profile of the impacted projectile. The technique involves unique features in addition to surface tilt insensitivity. These include a mode matching scheme which permits the use of high power, multilongitudinal mode lasers where formerly a single frequency laser was required. Experimental results are presented and compared with independent accelerometer measurements.

An improvement to the saturated absorption technique of long term stabilization of lasers is reported. This new method enables stabilization to the centre of saturated absorption features regardless of whether the peaks are symmetric or asymmetric. Another feature of the locking system is its ability to stabilize the laser at precisely known small detunings from the centre of the absorption line. The locking system has been applied to both dye laser and titanium sapphire laser systems. The long term drift for each was measured to be smaller than the laser jitter bandwidth of about 1 MHz for periods of hours, and no mode hops were recorded over several weeks of operation.

A coincidence data acquisition system, incorporating a position sensitive detector and a custom-built data acquisition card installed in an IBM-PC 486 computer, has been implemented in a coincidence experiment in which scattered electrons and Auger electrons are detected in coincidence. Three analog-to-digital converters (ADCs) are used to digitize all the timing and energy information, and custom-designed and written control software is used to accumulate the data, display it in real time, and store it in expanded memory. The new system has ben used to measure the energy and angular distribution of Auger electrons ejected from argon after electron impact ionization.

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